1. Field of the Invention
This invention relates to a printing method and apparatus which is capable of controlling a printing operation in a manner adapted to a fixed print length.
2. Prior Art
A printing apparatus generally employed with a word processor or the like usually prints on paper cut to a predetermined size(cut sheet). To print on such cut sheets, the size of paper to be printed by the printing apparatus is set to a selected standard size or an arbitrarily set size, which is equal to the predetermined size, and a print range (length of a print area in the direction of feed of the paper (printing length) and length of the same in the direction of a lateral line of printed characters) or margin widths (margin lengths) in longitudinal (front-rear) and lateral directions are set to predetermined values, and then a desired print image is printed according to the predetermined values.
There is also used another type of printing apparatus which principally prints on a continuous sheet of paper over a desired length. A typical example of this type of printing apparatus is a tape printing apparatus. Some of tape printing apparatuses are also known to be capable of forming a label or the like which has a predetermined length by setting length (tape length) of a print material (tape) and front and rear margins (front margin length and rear margin length) of the same and after the printing, cutting off the tape at a predetermined cutting position.
In addition to these printing apparatuses, facsimile machines can be also classified into the above two types of printing apparatuses. That is, a type of facsimile machine which prints the received facsimile image on a sheet of paper having a predetermined size can be counted among the printing apparatuses of the first-mentioned type (which prints on cut sheets) while another type which prints the received facsimile image on a roll of continuous paper to be dispensed among the printing apparatuses of the second-mentioned type (which prints on a continuous sheet of paper). Further, a type of cash register which prints details of prescribed items (image thereof) on a sheet of receipt and provides a predetermined margin thereafter is classified into the latter type, and a ticket machine which prints an image of predetermined contents of a ticket on a continuous sheet of paper and then cut off the sheet for delivery is also classified into the latter type.
These types of printing apparatuses require accurate position control, in other words, a so-called fixed length control for adapting a printing operation to a predetermined length of a print material (print medium). More specifically, it is required that based on a definite length of the print material (length in the direction of feed of the paper (cut sheet) in the case of the former type and length from a front end of the paper (continuous sheet) to a cutting position of the same in the case of the latter type), a front margin length, a print length, and a rear margin length, first, a front margin is set from the front end of the print material, and printing is started from a print start position or the rear end of the front margin, and carried out through the print length, followed by providing the rear margin. In the case of the latter type, it is further required that the print material is cut at the cutting position which is set to the rear end of the rear margin.
To attain the accurate fixed length control, many of the printing apparatuses employ, a stepping motor (pulse motor) which can be controlled in respect of speed (constant speed control) based on the number of pulses, a so-called DC servomotor which incorporates a constant speed control circuit, or the like, as a drive source for driving relative motion means for moving at least one of the print head and the print material relative to the other, to thereby cause relative motion between them at a constant or controlled speed of the relative motion from the start of the motion.
That is, since the speed of the relative motion is constant, the printing of the print image is started when a predetermined time period corresponding to the predetermined front margin length elapses after the time point of the start of the relative motion between the print head and the print material, to continue the printing through the predetermined print length at the constant speed, and then the relative motion between the print head and the print material is carried out for a time period corresponding to the predetermined rear margin length to stop the relative motion between them.
Particularly as to the latter type, to cut off the print material at a cutting position where the relative motion for the printing of the print material is stopped, the print material is required to be stopped accurately at the stop position adapted to the predetermined print length, and hence, the stepping motor is generally employed as the drive source for this type of printing apparatus. More specifically, in this case, not only the constant speed control but also accurate stopping control is necessitated, and therefore, the stepping motor is employed since it can cause the printing operation to be stopped accurately at a desired position only by stopping the supply of pulses.
As described above, in the conventional printing apparatuses, as the drive source for carrying out the fixed length control (print control, position control, and speed control), a relatively expensive motor, such as a stepping motor, is required to be used, and this hinders the manufacturing costs of the printing apparatuses from being reduced.
On the other hand, when a DC motor, which is relatively inexpensive, is used as the drive source for driving means for the relative motion between the print head and the print material, since the DC motor does not have a control circuit for constant speeds, it cannot attain the constant speed of the relative motion. Particularly, when the printing is started or terminated, the speed of relative motion undergoes large variation due to acceleration at the start of printing and deceleration at the termination of the same, and hence it is impossible to apply the above-mentioned position control (print control and fixed length control) to be executed under the constant speed of the relative motion between the print head and print material.
Further, to stop the relative motion, it is required to turn off the DC motor, but only the turning-off of the DC motor is not enough for causing the relative motion to be stopped at the stop position adapted to the predetermined print length, since the DC motor continues to rotate for some time by inertia. Particularly, in the latter case (using the continuous sheet), the print material should be cut off by setting the stop position to a position where the print material is cut off, and hence incapability of stoppage at the position adapted to the predetermined print length, that is, implies incapability of the fixed length control, causes a large problem.